An Empirical Transmitted EPID Dosimetry Method using a Back-Projection Algorithm

J Biomed Phys Eng. 2019 Oct 1;9(5):551-558. doi: 10.31661/jbpe.v0i0.1082. eCollection 2019 Oct.

Abstract

Background: The present study aimed to introduce a rapid transmission dosimetry through an electronic portal-imaging device (EPID) to achieve two-dimensional (2D) dose distribution for homogenous environments.

Material and methods: In this Phantom study, first, the EPID calibration curve and correction coefficients for field size were obtained from EPID and ionization chamber. Second, the EPID off-axis pixel response was measured, and the grey-scale image of the EPID was converted into portal dose image using the calibration curve. Next, the scattering contribution was calculated to obtain the primary dose. Then, by means of a verified back-projection algorithm and the Scatter-to-Primary dose ratio, a 2D dose distribution at the mid-plane was obtained.

Results: The results obtained from comparing the transmitted EPID dosimetry to the calculated dose, using commercial treatment planning system with gamma function while there is 3% dose difference and 3mm distance to agreement criteria, were in a good agreement. In addition, the pass rates of γ < 1 was 94.89% for the homogeneous volumes.

Conclusion: Based on the results, the method proposed can be used in EPID dosimetry.

Keywords: Algorithms; Dose-Response Relationship; Radiotherapy; Radiotherapy Planning, Computer-Assisted.